1. Field of the Invention
The present invention relates to a packaging substrate to which a semiconductor chip is packaged, and a semiconductor device obtained by packaging a semiconductor chip to the packaging substrate.
2. Description of Related Art
Semiconductor devices of a flip chip bonding structure are hitherto known in which a semiconductor chip is bonded to a surface of a packaging substrate such as a printed wiring substrate in a face down manner.
In a semiconductor chip to be applied to such a semiconductor device of a flip chip bonding structure, a function surface thereof on which a function element is formed is coated with a passivation film. The passivation film is provided with a plurality of openings for partly exposing an internal wiring electrically connected to the function element as electrode pads. On each of the electrode pads, a metal ball of a fusible metal material such as solder is formed in a protruded manner. On the other hand, a surface of the packaging substrate is coated with a solder resist layer for protecting a wiring. The solder resist layer is provided with openings for partly exposing the wiring at the positions respectively corresponding to the electrode pads of the semiconductor chip.
Thus, the semiconductor chip is bonded to the surface of the packaging substrate with the function surface of the semiconductor chip opposed to the surface of the packaging substrate. Each metal ball is connected through the corresponding opening to the wiring on the packaging substrate, so that the semiconductor chip and the packaging substrate are connected with a predetermined distance therebetween and electrically connected to each other. Thereby, a semiconductor device of a flip chip bonding structure can be obtained.
However, the sizes (volumes) of the metal balls are not always strictly uniform with one another but somewhat different. Therefore, in a semiconductor device of a flip chip bonding structure, sometimes there occurs a problem that a semiconductor chip 102 is bonded to a packaging substrate 101 in an inclined manner as shown in FIG. 4. Especially in an ultra small semiconductor device to which a WL-CSP (Wafer Level-Chip Scale Package) technology has been applied, such a problem caused by the difference between the sizes of metal balls 103 remarkably appears.